The president's first speech to a joint session of Congress in 2009 - technically not a State of the Union but serving a similar function - drew 52.4 million television viewers.

The TV audience for Obama has steadily declined every year since.

In terms of social media, Nielsen SocialGuide reported that 8.8 million people saw at least one of the 2.1 million tweets sent in the USA about the 2014 State of the Union speech.

"Twitter activity about the airing spiked at 9:47 p.m., with 32,918 Tweets sent following the president's reference to 'equal pay,' " reported Nielsen SocialGuide, which measures such activity around television shows and events.